Gem stone polishing machine



July 14, 19 70 A. LEiBOWlTZ 3,520,088

I GEM STONE POLISHING MACHINE Filed Dec. 15, 1967 //VV[/V7WP ALEC LEIBOWITZ 9) United States Patent 3,520,088 GEM STONE POLISHING MACHINE Alec Leihowitz, London, England, assignor to Spectrum Diamonds (Proprietary) Limited, Johannesburg, Republic of South Africa, a company of Republic of South Africa Filed Dec. 15, 1967, Ser. No. 690,915 Claims priority, application Great Britain, Dec. 20, 1966, 56,978/ 66 Int. Cl. B24b 7/00, 19/00 US. Cl. 51122 Claims ABSTRACT OF THE DISCLOSURE A machine for automatically faceting gem stones which enables a complete ring of facets to be formed on a stone automatically, the machine having a control system for automatically polishing each facet to the same depth and automatically indexing the stone to different facet forming positions between each polishing operation.

This invention relates to gem stone shaping, in art which is concerned with processing a stone until it is ready for sale to the public. In this specification, the words gemstone include such elements as natural or artificial rubies, emeralds, semi-precious stones, diamonds, hard glasses and the like.

In a common form of treatment say, a diamond, the uncut stone is firstly equipped with a girdle zone which distinguishes the top of the stone from the base area. Thereafter the stone is gripped in a pot for subsequent attachment to a dop which in turn is anchored to a tang. The tang is then used as a means of maintaining the gem in contact with a polishing wheel which is usually made of cast iron impregnated with diamond particles. When a facet is developed in the gem, the next facet can only be started by changing the location of the stone relative to the wheel. It is customary practice for the polishing of a facet to be accompanied by a zooting motion of the gem over the wheel surface. This means that the tang is given a radial oscillating movement over the wheel surface.

The present invention consists in apparatus for faceting a gem stone comprising a tang, a chuck mounted on the tang, the chuck being adapted to carry a gem stone or a gem stone in a holder with the stone axis inclined to the tang, and the chuck being adapted for rotational motion about the stone axis and orbital motion about another axis substantially perpendicular to the tang and control means for automatically and cyclically effecting a sequence of operations to facet the stone including allowing the stone to contact a polishing surface to develop one facet on the stone, moving the tang away from said surface when said one facet has been polished to a predetermined depth, indexing the chuck about the stone axis through a predetermined range of movement suitable for developing another facet on the stone, causing the tang to move towards said surface and contact said surface to develop said another facet and again moving the tang away from said surface when said another facet has been polished to the same predetermined depth as said one facet.

In a preferred form of the invention, the apparatus includes means for continuously reciprocating the chuck over the polishing surface during polishing to effect a smoothing action conveniently in the form of automatically reversing motor means for reciprocating the tang in its longitudinal direction. This reciprocating motion of the tang may be accompanied by reciprocatory orbital motion of the chuck about said another axis.

To effect lifting of the tang for terminating polishing 3,520,088 Patented July 14, 1970 when each facet has received the same predetermined depth of polishing, the control means may include means establishing an electrical conducting path by contact of the chuck or stone holder with the polishing surface and tang lifting means operative in response to the establishment of said conducting path.

According to a further feature of the invention, the control means may include means for automatically coordinating the orbital position of the chuck relative to said another axis with the rotational position of the chuck relative to the stone axis so that each facet will be polished in a predetermined polishing direction which is necessaly in diamond polishing.

Also according to the invention means to index the movement of the chuck about the stone axis includes a suitable form of electric circuit coupled to the chuck in such a way as to ensure only unidirectional stepped rotational motion of the chuck. Preferably, the means to move the chuck about the stone axis is adapted to operate on an automatic basis according to a predetermined pattern but is capable of being controlled by an operator with a view to amending the pattern.

An auxiliary control arrangement may be provided at a strategic point for an operator so that movement of the stone above the two axes may be adjusted to suit requirements. Preferably, the control arrangement includes a switch bank, the bank allowing any selected zone of the gem to be worked through rotation of the chuck about the stone axis and which allows for changes to be made in the direction of polishing by moving the gem in the orbit about said another axis. The auxiliary control arrangement may be subordinate to the control means which automatically moves the stone around its axis in a step-by-step movement, each step corresponding to a particular facet on the stone.

Preferably, movement of the chuck can also be accomplished by the operator through the switch bank or the like independently of the operation of the control means.

The lowering of the chuck is an automatic step following adjustments in the angular setting of the stone relative to the abrading surface and in regard to the means for lowering the chuck a cushioning arrangement such as a dashpot control system may be employed to ensure that the stone makes a gentle contact with the surface.

An electric motor may be employed to oscillate the tang over the grinding surface. Preferably, the arrangement is one in which a carriage is oscillated in or on a track and the tang engages a carriage element, tongue and groove fashion, so that the tang may be removed to inspect the progress made on the gem without having to stop the device.

In order to illustrate the invention, an example is described hereunder with reference to the accompanying drawing, which is a composite view of a polishing machine showing the mechanical components in perspective and an automatic control system therefor in block diagram form.

A tang 1 includes a metal bar 2 which at one end is equipped with a claw arrangement 3 for engaging over a bar 4 on a carriage 5 and at the other end provides a pivot 6 perpendicular to the tang for a depending chuck. The chuck 7 is capable of moving in an orbit about the axis defined by the pivot -6 through the agency of an electric motor 8 anchored to the tank, the axis being perpendicular to a grinding wheel 9. In addition, the chuck is capable of rotating about a further axis 10 which is inclined to the surface of a polishing, abrading or grinding wheel or disc located beneath the chuck. The inclined axis passes through the centre of a gem held by a holder in the chuck and the purpose of rotating the leading end of the chuck about the inclined axis is to present different parts of the gem to the abrading surface for the production of different facets on the stone. ,A gem holder of the type described in South African patent application No. 66/0624 may be used to hold a stone in the chuck. Thus, when the stone first engages the abrading surface a first facet is developed. If now the chuck is turned through, say 20 degrees about the stone axis, then the apparatus will now ensure the development of a second facet on the stone, and so the process proceeds until a whole ring of facets is produced.

Also, the chuck is mounted on a pivoted bracket 11 to provide means for adjusting the inclination of the chuck, i.e. the inclination of the stone axis to the tang so that different rings of facets requiring different polish ing angles can be developd.

The carriage is mounted on a base 12 through rollers 13 guided in tracks 14, and an automatically reversing double acting hydraulic piston and cylinder 15 is connected to the carriage for reciprocating the latter across base 12 to effect continuous reciprocation of the stone across the wheel during polishing. For example, when the piston and cylinder is operating, a trip can be arranged to be operated by the piston at each end of its stroke to reverse the cylinder valving arrangements. A single acting pneumatic piston and cylinder assembly 16 anchored to the base 12 is provided for lifting the tang between faceting operations as will be described.

The arm 2 of the tang has a downwardly depending follower 17 adapted to press on a dashpot assembly 18 as the tang is being lowered towards the wheel to cushion the downward motion of the tang, the arrangement being such that a floating member 18a of the dashpot is depressed by the tang as the tang is lowered and this member rises when the tang is lifted.

It has been established in diamond polishing that particular facets can usually be polished in directions bearing an angular relationship. For example, for a diamond which is to have eight facets with adjacent facets numbered in sequence F1 F8, then facets F2 to F8 can each be polished in a particular direction relative to a direction suitable for polishing facet F1. Accordingly, having established this polishing direction for facet F1, the remaining facets can each be polished at a particular orbital position of the chuck about axis 6 relative to the orbital position about this axis for polishing facet F1. Therefore, the machine can be programmed to correlate the position of the chuck about its own axis with its position about the vertical axis 6 between each polishing operation. This aspect of the invention, and the control system as a whole, will be described with reference to the working cycle of the machine.

Assuming a ring of eight facets F1 to F8 is to be developed on a diamond, then section B of a control unit C.U., which section controls the chuck position, will be programmed to index the chuck in steps of 45 degrees about axis 10 between each facet polishing operation to develop adjacent facets successively, and to index the chuck about vertical axis 6 in unidirectional steps, the magnitude of which and interval between which are dependent on the polishing direction required for the successive facets.

To commence polishing, an operation positions a stone in a holder in the chuck and sets bracket 11 at an inclination suitable for the polishing angle required for the ring of eight facets. The carriage 5 is set reciprocating through an actuating mechanism D of the control units which effects automatic and continuous reciprocatory operation of the piston and cylinder 15. The tang is gently lowered onto the wheel by pressing on dashpot 18, and then a suitable polishing direction is established manually for the first facet and the orbital position of the chuck relative to vertical axis 6 is manually set accordingly. Then, the automatic control sections A, B and C can be operated because the polishing directions for the remaining facets will all have fixed angular relationships 4 to that of the original facet which will be established by the control system.

Having actuated sections A, B and C of the control unit, automatic operation proceeds as follows:

Polishing of the first facet continues until the gem holder contacts the polishing wheel. The holder has an electrical connect a through the chuck to section A of the control system, and the wheel also has a connection b to section A. Thuswhen the holder contacts the wheel, a circuit is established which through a suitable relay and a circuit C signals piston and cylinder 16 to rise, to lift the tang off the wheel.

When the tang has lifted, another relay, which could be operated directly from piston 16, activates section B of the control system to index the chuck about axis 10 through 45 degrees for polishing the succeeding facet, and to index the chuck about axis 6 by an amount suitable for establishing the correct polishing direction for this succeeding facet. Should a pair of succeeding facets be capable of being polished in the same direction or if the chuck is indexed about axis 10 in steps of more than one facet then the orbital position of the chuck would not be altered between succeeding polishing operations. This would be taken care of by suitable programming of section B of the control system. Any known form of automatic programmer can be used.

To effect accurate indexing of the chuck about axes 6 and 10, the programmer can be operated on a time base with controls d and 2 leading respectively to constant speed motors 8 and 20 adapted through the programmer to rotate the chuck about the respective axes for a set time. To improve accuracy the motors can be coupled to the chuck through speed reduction means.

When section B has completed the indexing movements of the chuck, it operates a further relay actuating section C of the control unit which signals cylinder 16 to lower and thus again bring the tang down onto the wheel to polish the next facet. A relay operated by piston 16 can then again activate section A of the control unit so that when the holder again touches the wheel, signifying the completion of polishing of the second facet, the tang will again lift. Thus, the process is automatically repeated for all eight facets.

A counting mechanism can be included in the control unit to stop the machine when all facets have been polished and/or to actuate a visible or audible signal on completion of all eight facets to alert the operator.

I claim:

1. Apparatus for automatically developing a plurality of facets on a gem stone comprising a tang, a chuck mounted on the tang adapted to carry a gem stone or a gem stone in a holder with the stone axis inclined to the tang, the chuck being capable of rotational motion about the stone axis and orbital motion about another axis substantially perpendicular to the tang, means for lowering the tang towards a polishing surface, means for lifting the tang away from the polishing surface, first indexing means for rotating the chuck in faceting steps about the stone axis, second indexing means independent of the first indexing means for orbiting the chuck about said another axis to alter the polishing direction and automatic control means for repeatedly operating the lifting and lowering means of the first and second indexing means to successively develop a plurality of facets on the stone, the control means including means for automatically operating the tang lifting means when each facet has been polished to the same predetermined depth,means for automatically operating the first indexing means between each successive faceting operation and means for automatically operating the second indexing means in unidirectional steps between at least some successive facetmg operations, the magnitude of said unidirectional steps being dependent on the polishing direction required by succeeding facets.

2. Apparatus as claimed in claim 1, wherein the control means includes programmed means establishing a preset pattern of movements of the chuck about the stone axis and said another axis between successive faceting operations means for operating the first indexing means between each successive faceting operation and means for operating the second indexing means between at least some successive faceting operations if required in accordance with said pattern.

3. Apparatus as claimed in claim 1 including means for continuously reciprocating the chuck over the polishing surface during polishing to effect the smoothing action.

4. Apparatus as claimed in claim 3, wherein the means of continuously reciprocating the chuck comprises automatically reversing motor means for reciprocating the tang in its longitudinal direction.

5. Apparatus as claimed in claim 1, wherein the control means includes means establishing an electrical con- References Cited UNITED STATES PATENTS 9/1948 Spira 5l--229 8/1944 Simons 51-122 HAROLD D. WHITEHEAD, Primary Examiner US. Cl. X.R.

Dedication 3,520,U88.Alee Lez'bowz'te, London, England. GEM STONE POLISHING MACHINE. Patent dated July 14, 1970. Dedication filed Sept. 7 1973, by the assignee, Spectrum Diamonds (Proprietary) Ltd. Hereby dedicates the entire remaining term thereof to the Public.

[Oficz'al Gazette December 11, 1.973.] 

